1. Field of the Invention
The present invention relates to a power distribution and management system for use in a portable computer and packet-switched data radio combination.
2. Background Art
Power consumption in an electronic device is typically of significant concern as a power supply must be designed to adequately power the device and, where the power supply of the electronic device is powered up by a rechargeable battery, the battery life should preferably be as long as is reasonably practical. The practical aspect of battery life is particularly seen in laptop, palmtop and other portable computers wherein the power supply constitutes a major contribution to the overall size and weight of the portable computer. Aside from the capability of the power supply to supply ample power for the portable computer, heat dissipation, physical size, efficiency and other related characteristics are also important in designing or selecting the power source. All these factors become exceptionally important and perhaps even critical when designing a portable computer such as a laptop computer.
In typical portable computers, a battery is used to provide the power thereto when the portable computer is disconnected from an external power source. The battery provides auxiliary power to maintain certain critical circuits active, such as keeping the memory alive so as to retain any information stored therein. The battery must also function as the main power source to fully power the portable computer for a number and variety of power consuming functions. These functions merit additional power consumption rate considerations. For example, ROM and RAM memory devices, which include volatile and nonvolatile memories, diskette drives, hard disk drives, and display screens, all typically require a stable power source.
In the design of a power supply system for a portable computer, the objective to be maximized is to extend the self-sustaining time period during which the portable computer may be used, while the constraint to be minimized is the size and weight of the battery and power supply circuitry thereof. Sophisticated power management systems have been developed to provide power only to those circuits and devices which require such power and to remove power, or at least to cause a given circuit to enter a low power consumption mode, when that circuit is not needed. Such management systems must also continually monitor all the various circuits and devices in order that power can be applied immediately to activate such circuits and devices when needed.
An additional frontier in portable computing is the object of providing a variety of modular tools to be employed by the user so as to be, in effect, a mobile office. Such tools, which are added on to the portable computer in modules, comprise ever more sophisticated software such as spread sheets, contact managers, personal information managers, various business and industrial applications software, and general purpose word processors having both a dictionary and a thesaurus. The modular tool by which the increasing sophistication of the software is accommodated is ever more powerful processors such as those known in the art as the 386, the 486 and the 586 microprocessors.
To further expand the goal of achieving a mobile office environment, and in addition to software and the hardware therefor, portable computers are being modularly coupled with a variety of peripherals. Adding a modular peripheral to the portable computer is desirable because such a peripheral is conventional and perhaps essential in a typical office environment. By making the peripheral a modular addition to the portable computer, the resultant essentially singular unit is both compact and convenient. Peripherals that have been modularized include devices such as modems, telefacsimile machines, printers and packet-switched data radios.
As the goal of creating a mobile office environment in a modularized portable computer is increasingly realized, the power consumption requirements will concomitantly increase as well. Despite the advantages of lower power consumption in large scale integration and the electrical efficiency achieved in semiconductor technology, power management in portable computers remains an obstacle.
Particularly acute in power consumption management design is the overall size and weight of the portable computer plus the attached modular peripherals. The combined weight of each battery which supplies power to each respective peripheral module makes a significant contribution to the overall weight. The main power supply supplying power to the portable computer typically has a limited power output. For example, the maximum current output by a portable computer for purposes of powering an attached modular peripheral is generally between 30 milliamps and 1 amp.
In contrast, the power requirements for an attached modular peripheral may be significantly different. Most portable computers could not ordinarily supply enough power to peripherals with high power consumption requirements. An example of such a peripheral is the transmitter component of a packet-switched data radio. Packet-switched data radios place certain requirements on their power supplies. When transmitting, packet-switched data radios require a relatively high amount of power. At other times, such as when the radio is receiving data or is idle, the radio produces a relatively low drain on the power supply.
A typical solution to such a problem would be to provide a separate battery or other rechargeable power supply capable of providing to that peripheral a higher power output than that which the battery powered power supply of the portable computer is capable of providing. However, the use of separate batteries for the various peripheral modules on the portable computer increases both the overall size and weight of the portable computer/peripheral combinations. Furthermore, use of a separate secondary battery for the peripheral requires the user to worry about keeping both the main computer battery and the separate peripheral secondary battery charged. Not only must both the primary and the secondary battery remain charged, but separate charging equipment must accompany each battery when the portable computer is taken off-site. Not only must the user contend with the transportation of the extra charging equipment, but the user must also monitor the disparity in the charges of the two batteries. For example, if the peripheral device is used heavily, the battery supplying the power to the peripheral device may require charging earlier than the primary computer battery. As a result, the laptop, although fully charged, may become functionally useless because of the inability of the peripheral device to function properly. Conversely, heavy use of the computer may result in a discharged primary computer battery, thereby rendering the computer non-functional despite a full charge in the secondary peripheral battery.
Another obstacle in the past is that it is relatively difficult to monitor when a rechargeable battery is fully charged. In typical recharging circuits found in the prior art, the temperature rise of the battery is monitored until the battery temperature reaches a level indicating a fully charged condition, signalling that it is time to stop (or at least slow to a minimum) the recharging process. Such an approach is, however, a very energy inefficient process and often drains much more energy out of the system than it puts back into the rechargeable battery as useful energy.